A crag is a high, very steep mass of rough rock — not a pebble, not a smooth cliff you might walk along, but a torn, sticking-out place of stone, the kind a goat might stand on, or a castle might use as a wall against enemies. The word paints a wild picture: sharp, high, a little dangerous, with little soil and a long drop. Walkers, climbers, and story-writers like it because you can see it at once. It is a thing-word, a little literary in everyday city talk, completely at home in hills and coasts. It is not a thin break in a surface (that is a crack), and it is not the man’s name Craig, even though that name comes from the same old rock-word in Gaelic. English took it in the Middle Ages from a Middle Irish word for a rock. Some people have linked it, further back, to a very old word for “stone” or “hard”; that last step is only a maybe, and you do not need it to use crag.